Porsche had been using 911 R for racing but, because they had not homologated it, they were forced to run it as a prototypes. In 1968 they decided to homologate the 911 properly. As you were allowed to run any engine available in the bodyshell, they elected to homologate 911 T and not 911 S because the 911 T was 50 kilos lighter. Once homologated, they produced 36 911 T/R's. The T/R differed from a standard T with slightly wider wheelarches, no soundproofing, stiffened and lightened bodyshell, lightweight interior, long range fuel tank and extra oil coolers. They could be bought with a standard 911 S engine, an uprated 911 S engine or a 906 race engine.